CONTAINERS HAVING CROSSLINKED BARRIER LAYERS AND METHODS FOR MAKING THE SAME
DETAILED DESCRIPTION
TECHNICAL FIELD
[0001] The current invention preforms, containers, and other articles having layers containing crosslinking materials.
TECHNICAL BACKGROUND
[0002] Preforms are the products from which articles, such as containers, are made by blow molding. A number of plastic and other materials have been used for containers and many are quite suitable. Some products such as carbonated beverages and foodstuffs need a container, which is resistant to the transfer of gases such as carbon dioxide and oxygen. Coating and layering of such containers with certain barrier or adhesive materials has been suggested for many years. A resin now widely used in the container industry is polyethylene terephthalate (PET), by which term we include not only the homopolymer formed by the polycondensation of [beta]-hydroxyethyl terephthalate but also copolyesters containing minor amounts of units derived from other glycols or diacids, for example isophthalate copolymers.
[0003] The manufacture of biaxially oriented PET containers is well known in the art. Biaxially oriented PET containers are strong and have good resistance to creep. Containers of relatively thin wall and light weight can be produced that are capable of withstanding, without undue distortion over the desired shelf life, the pressures exerted by carbonated liquids, particularly beverages such as soft drinks, including colas, and beer.
[0004] Thin-walled PET containers are permeable to some extent to gases such as carbon dioxide and oxygen and hence permit loss of pressurizing carbon dioxide and ingress of oxygen which may affect the flavor and quality of the bottle contents. In one method of commercial operation, preforms are made by injection molding and then blown into bottles. In the commercial two-liter size, a shelf life of 12 to 16 weeks can be expected but for smaller bottles, such as half liter, the larger surface-to-volume ratio severely restricts shelf life. Carbonated beverages can be pressured to 4.5 volumes of gas but if this pressure falls below acceptable product specific levels, the product is considered unsatisfactory. Many of the materials used to make plastic containers are also susceptible to water vapor. The transmission of water vapor into the containers often results in the rapid deterioration of the food stuffs packaged within the container.
[0005] Thus, it is important that the surfaces and various layers of containers provide an effective barrier against gas and/or water permeability. Furthermore, it is desirable for the surface of such containers to be abrasion and scratch resistant.
DISCLOSURE OF THE INVENTION
[0006] Some embodiments described herein are directed to a method of crosslinking a coating layer on a container. This method can include applying a coating material on a preform to form a coating layer, the coating material having at least a first ethylenically unsaturated moiety and a crosslinking initiator, blow molding the preform into the container, exposing a surface of the coating layer to actinic radiation, and crosslinking the first ethylenically unsaturated moiety with a second ethylenically unsaturated moiety.
[0007] Some embodiments disclosed herein are directed to a method of producing a coated container. This method can include applying a coating material including a UV-sensitive photoinitiator and a compound selected from an acrylic monomer, an acrylic grafted polyurethane, and a polycarbonate-containing polyurethane polymer, on a preform to form a coating layer, blow molding the preform into a container, and curing the coating layer with UV irradiation.
[0008] Some embodiments disclosed herein are directed to a method of forming a container having multiple coating layers from a preform with a substrate layer. This method can include applying a first coating to a preform, drying the first coating to form the first coating layer, applying a second coating to the first coating layer, drying the second coating to form the second coating layer, wherein at least one of the first or second coatings includes a compound having an ethylenically unsaturated moiety capable of crosslinking upon exposure to actinic radiation, and wherein at least one of the first or second coating layers has a permeability to oxygen and carbon dioxide less than the substrate layer, exposing the first and second coatings to actinic radiation, and crosslinking the layer comprising the compound.
[0009] Some embodiments disclosed herein are directed to a container that may have a substrate layer for contacting foodstuffs, which also includes a gas barrier layer, the gas barrier layer including a semi-interpenetrating polymer network, the semi-interpenetrating polymer network including a gas-barrier material selected from PVOH, EVOH, co- or ter-polymers of PVOH and EVOH, a phenoxy-type thermoplastic, and combinations thereof, and the curing product of an ethylenically unsaturated monomer.
[0010] Some embodiments disclosed herein are directed to a preform that can include a substrate layer and a gas barrier layer, the gas barrier layer including a gas-barrier material having a permeability to oxygen and carbon dioxide less than the substrate layer, a first UV curable ethylenically unsaturated moiety, and a first UV photoinitiator, the first moiety capable of forming a semi interpenetrating polymer network with the gas barrier material upon exposure to UV radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 is an uncoated preform as is used as a starting material for preferred embodiments.
[0012] Figure 2 is a cross-section of a preferred uncoated preform of the type that is coated in accordance with a preferred embodiment.
[0013] Figure 3 is a cross-section of one preferred embodiment of a coated preform.
[0014] Figure 4 is an enlargement of a section of the wall portion of a coated preform.
[0015] Figure 5 is a cross-section of another embodiment of a coated preform.
[0016] Figure 6 is a cross-section of a preferred preform in the cavity of a blow-molding apparatus of a type that may be used to make a preferred coated container of an embodiment of the present invention.
[0017] Figure 7 is a coated containerprepared in accordance with a blow molding process.
[0018] Figure 8 is a cross-section of one preferred embodiment of a coated container having features in accordance with the present invention.
[0019] Figure 9 is a three-layer embodiment of a preform.
[0020] Figure 10 there is a non-limiting flow diagram that illustrates a preferred process.
[0021] Figure 11 is a non-limiting flow diagram of one embodiment of a preferred process wherein the system comprises a single coating unit.
[0022] Figure 12 is a non-limiting flow diagram of a preferred process wherein the system comprises multiple coating units in one integrated system.
[0023] Figure 13 is a non-limiting flow diagram of a preferred process wherein the system comprises multiple coating units in a modular system.
[0024] Figures may not be drawn to scale.
PREFERRED EMBODIMENTS OF THE INVENTION
[0025] Articles having one or more layers comprising crosslinked materials and methods of making the same are described herein. In particular embodiments, the articles may possess UV-cured or UV-curable coating layers. In some embodiments, a UV-curable coating layer may include a suitable photoinitiator and a compound having an ethylenically unsaturated moiety. Upon exposure to UV radiation, the ethylenically unsaturated moiety reacts with other ethylenically unsaturated moieties to produce crosslinking between compounds. Such reaction cures the material in the coating layer to produce the UV-cured coating layer.
[0026] Unless otherwise indicated, the term “article” is a broad term and is used in its ordinary sense and includes, without limitation, wherein the context permits, plates, molded or hollow bodies, pipes, cylinders, containers, tubes, blanks, parisons, and performs. Alternatively, embodiments of the articles could take the form of jars, tubes, trays, bottles for holding liquid foods, medical products, or other products, including those sensitive to oxygen exposure or other effects of gas transmission through the container. Unless otherwise indicated the term “container” is a broad term and is used in its ordinary sense and includes, without limitation, both the preform and bottle container therefrom. The processes as described herein generally are used on preforms or in the formation of preforms. In some embodiments, the processes are used on bottles or other articles, or in the formation of such articles.
[0027] Certain coating processes as described herein generally are used on preforms. However, the coating processes may also be used on other articles such as containers (e.g, bottles, pouches), or in the formation of such articles. As presently contemplated, one embodiment of an article is a preform of the type used for beverage containers. However, for the sake of simplicity, these embodiments will be described herein primarily as containers or preforms.
[0028] The articles described herein may be described specifically in relation to a particular substrate, such as polyethylene terephthalate (PET), but preferred substrate materials are applicable to many other thermoplastics. In one embodiment, PET is used as the polyester substrate. As used herein, “PET” includes, but is not limited to, modified PET as well as PET blended with other materials, such as IPA.
[0029] As used herein, the term “substrate” is a broad term used in its ordinary sense and includes embodiments wherein “substrate” refers to the material used to form at least a portion of the article. In certain embodiments, substrate refers to the material used to form the base layer of the article. Other suitable substrates include, but are not limited to, various polymers such as polyesters (PET, PEN, PETG), polyolefins (PP and PE), polyamides (Nylon 6, Nylon 66), polycarbonates, polylactic acid (PLA), acrylics, polystyrenes, epoxies, grafted polymers, and copolymers or blends of any of the foregoing. In certain embodiments preferred substrate materials may be virgin, pre-consumer, post-consumer, regrind, recycled, and/or combinations thereof.
[0030] In one embodiment, PET is used as the polyester substrate which is coated. As used herein, “PET” includes, but is not limited to, modified PET as well as PET blended with other materials. One example of a modified PET is “high IPA PET” or IPA-modified PET. The term “high IPA PET” refers to PET in which the IPA content is preferably more than about 2% by weight, including about 2-10% IPA by weight.
[0031] As used herein, the terms “crosslink,” “crosslinked,” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to a process of establishment of chemical links between chains of molecules, resulting in a tridimensional network that has greater strength and less solubility compared to the non-crosslinked monomers. As used herein, crosslinked materials and coatings vary in degree from a very small degree of crosslinking up to and including fully cross linked materials such as a thermoset epoxy. The degree of crosslinking can be adjusted to provide the desired and/or appropriate physical properties, such as the degree of chemical or mechanical abuse resistance for the particular circumstances.
[0032] As used herein, the terms “barrier material,” “barrier resin,” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to materials which, preferably adhere well to the article substrate and/or one or more other layers. Barrier materials may include “gas barrier materials” which refers to one or more materials having a lower permeability to oxygen and/or carbon dioxide than one or more of the other layers of the finished article (including the article substrate). Barrier materials may also refer to “water-resistant barrier materials” which refers to one or more materials having a lower water vapor transmission rate or high water resistance than the article substrate. As used herein, the terms “UV protection” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to materials which, when used to coat articles, preferably adhere well to the article substrate and have a higher UV absorption rate than one or more other layers of the article. As used herein, the terms “oxygen scavenging” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to materials which have a higher oxygen absorption rate than one or more layers of the article. In some embodiments, oxygen scavenging materials adhere well to one or more layers of the article. As used herein, the terms “oxygen barrier” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to materials which are passive or active in nature and slow the transmission of oxygen into and/or out of an article. As used herein, the terms “carbon dioxide scavenging” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to materials which have a higher carbon dioxide absorption rate than one or more layers of the article. In some embodiments, carbon dioxide scavenging materials adhere well to one or more layers of the article.
[0033] As used herein, the terms “water-resistant,” “water-repellant” and the like are broad terms and are used in their ordinary sense and refer, without limitation, to characteristics of certain material which results in the reduction of water transmission through the material. In an embodiment, it refers to the reduction of the rate of water transmission. In some cases, it also refers to the ability of the material to remain substantially chemically unaltered upon exposure to water in its solid, liquid, or gaseous states at various temperatures. It may also include the ability of certain materials to further impede access of water to materials which are water sensitive or which degrade upon exposure to water. As used herein, the term “chemical resistance” and the like is a broad term and is used in its ordinary sense and refers, without limitation, to characteristics of certain materials to remain substantially chemically unaltered upon exposure to chemicals, including water, whether in their gaseous, liquid, or solid state, including, but not limited to, water.
[0034] One or more layers of coating materials are employed in methods and processes disclosed herein. The layers may comprise one or more barrier layers, one or more UV protection layers, one or more gas barrier layers, one or more oxygen scavenging layers, one or more carbon dioxide scavenging layers, one or more water-resistant layers, and/or other layers as needed for the particular application. In one embodiment, an article comprises one or more water-resistant coating layers and one or more gas barriers layers, wherein the gas is oxygen or carbon dioxide.